1. Field of the Invention
The present invention relates to a power generation apparatus for converting kinetic energy (vibrational energy) into electric energy, and particularly to a vibration drive capacitive power generation apparatus that is manufactured by using micro electromechanical system (MEMS) technology.
2. Description of Related Art
FIG. 54 is a schematic diagram illustrating a conventional example of a vibration power generation apparatus that is manufactured by using the MEMS technology. The vibration power generation apparatus of the conventional example has a structure including an upper unit U1 and a lower unit U2 that are manufactured separately by using a bulk MEMS technology and then are glued to each other.
In FIG. 54, numeral 100 denotes parylene (registered trademark), numeral 101 denotes a silicon substrate, numeral 102 denotes a silica layer, numeral 103 denotes an electret, numeral 104 denotes an opposing electrode, numeral 105 denotes a base electrode, numeral 106 denotes Pyrex (registered trademark), and numeral 107 denotes a spacer.
The principle of operation of the vibration power generation apparatus having the above-mentioned structure is that an overlapping area between the electret 103 and the opposing electrode 104 is varied by vibration in the two dimensional plane direction (X direction and Y direction), and a variation of electric charge induced to the opposing electrode 104 is extracted as current.
Further, as a related art of the vibration power generation apparatus that is manufactured by using the MEMS technology, there is, for example, JP-A-2009-77614 (hereinafter referred to as Patent Document 1).
However, in the conventional vibration power generation apparatus described above, the generated power is approximately 10 μW, which can be used for a limited application.
In addition, the above-mentioned conventional vibration power generation apparatus has a structure in which the electret 103 and the opposing electrode 104 face each other. Therefore, if a gap distance between the upper unit U1 and the lower unit U2 is designed too small, electrostatic attraction acts between the electret 103 and the opposing electrode 104 so that they contact with each other, or injected electric charge of the electret 103 may be discharged. Therefore, the gap distance between the upper unit U1 and the lower unit U2 should be designed to be a certain value. However, in order to increase the gap distance and still to obtain a large variation of capacitance by the vibration, it is necessary to design areas of the electret 103 and the opposing electrode 104 to be large. As a result, it is required to increase the gap distance more. Because of this vicious circle, the above-mentioned conventional vibration power generation apparatus is designed, for example, to have a gap distance of approximately 70 μm and a lateral dimension of the electret 103 of approximately 150 μm. Therefore, there is plenty of room for improvement in downsizing the apparatus.
Further, in the above-mentioned conventional vibration power generation apparatus, electric charge injection (electrification) into the electret 103 is performed in a noncontact manner by using corona discharge (atmospheric discharge) before gluing the upper unit U1 and the lower unit U2 to each other. However, a large scale of corona discharge equipment is necessary for perform such the electric charge injection process, which is disadvantage in manufacturing cost.